The present invention relates to a brake shoe for elevator emergency stop, a device for elevator emergency stop and an elevator with an emergency stop function.
An elevator is provided with a device for emergency stop in order to prevent a fall due to unexpected breakdown of the elevator. The device for emergency stop comprises a cage elevated by an elevating means, an elastic member attached to the bottom part of the cage and having a U shape, capable of opening in a horizontal direction, a pair of plate-like guide members opposing each other and having outer surfaces contacting the end of the elastic member, respectively, and inner surfaces inclining such that a gap between the guide members gradually decreases toward the upper ends of the guide members, a rail which has a T-shaped cross section and positioned between the guide members and extending in a vertical direction, a pair of brake shoes provided in the gap between the guide members, arranged symmetrically with respect to the rail, capable of moving vertically along the inner surfaces of the guide member, and having braking faces opposing each other, and a pair of pulling means attached to the brake shoes, respectively, for pulling upward each the brake shoes. In such a device for emergency stop, if the cage falls due to the breakdown of the elevating means, the pulling means operates by detecting the falling speed of the cage to cause the elastic member to press the guide members so that the brake shoes pinches the rail and, as a result, the speed of the falling cage is reduced and the cage is stopped by the frictional force between the brake shoes and the rail.
Heretofore, the brake shoes have been made of such materials as cast iron or copper-based sintered alloys having suitable coefficients of friction and wear resistance. However, the recent demand for high-speed and large-capacity elevators because of high-rise buildings has brought about the problems of heat generation due to friction and decrease in the coefficient of friction. For example, the result of a simulation indicates that the localized temperature of the sliding face by friction exceeds 1000.degree. C. in the case where the moving speed of an elevator reaches 800 m/min. If such a temperature generates at the time when the elevator slows down and stops, the use of a brake shoe made of a metal becomes difficult in terms of strength and heat resistance. In addition, another problem is seizure because of the reaction between the brake shoe and the rail after slowing down and stop.
Based on the above-described background, Japanese Patent Application Publication (JP-B) No. 62-34,674 discloses the use of a brake shoe made by embedding a sliding member, which has a plurality of projections formed integrally with a ceramic plate having excellent heat resistance, in the braking face side of the metal body that faces a rail. However, since a plurality of the projections are formed integrally with a ceramic plate, the impact generated by the pinching of the rail at the time of slowing down and stop causes the breakdown of the root of the projections thereby remarkably decreasing the coefficient of friction of the projections, i.e., the braking effect diminishes. In addition, since the amount of wear of the ceramic material is very small, the friction property per unit number of the projections is not always satisfactory. As a result, instant slowing down and stop of the elevator at the time of emergency will become difficult.